The purpose of this project is to elucidate the mechanisms involved in recovery from vestibular injury (vestibular compensation) in primates. Experiments will focus on the physiological processes underlying recovery of the vestibulo-ocular reflex (VOR) following unilateral labyrinthectomy or plugging of the semicircular canals. The role played by volition in compensatory ocular responses during head movement will be investigated by analyzing unrestrained eye and head saccadic movements (head-free gaze shifts) before and after labyrinthine lesion. Single-unit recordings of neurons in the vestibular nuclei will be analyzed for changes in their oculomotor and angular acceleration sensitivity before unilateral labyrinthine lesion and after compensation. The hypotheses to be tested are that (1) passive vestibular compensation seen in vestibulo-ocular responses is the result of plasticity in the commissural connections between the bilateral vestibular nuclei; (2) the neurons found in the vestibular nuclei of the compensated animal carry the same oculomotor sensitivity as in the intact animal; and (3) the animal is able to utilize efference copies of neural signals which encode head movements and/or cervical feedback to facilitate behavioral compensation during natural, unrestrained head movements. This research is an outgrowth of the candidate's interest in vestibular compensation, which developed from his previous research experience and from his work as an otolaryngologist treating patients complaining of dizziness. The work in this proposal will be done under the direction of Dr. W. Michael King in collaboration with a diverse group of investigators who study vestibular and oculomotor function at the University of Mississippi Medical Center. To complement the work in the lab, the candidate will undergo instruction in computer function and programming and biostatistics to facilitate establishment of the candidate as an independent investigator/clinician studying plasticity in the vestibular system, particularly as it pertains to natural head movements.